The session timeout can be changed in nSerivce4/web.config.
<forms name=".ASPXAUTHnService4" loginUrl="Common/LogOnPage.aspx" protection="All" timeout="60" path="/" requireSSL="false" slidingExpiration="true" defaultUrl="Common/AdminHomePage.aspx" cookieless="UseCookies" enableCrossAppRedirects="false" >
<sessionState mode="StateServer" cookieless="false" timeout="60" stateConnectionString="tcpip=localhost:42424" >
The values are in minutes. Make sure the sessionState mode is "StateService". If it is "InProc", when nService gets restarted, all your sessions will be reset.